Lithography Mask Blank Ammonium Ion Preventing Layer
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Solution Overview
Problem
The production of ammonium ions on the surface of nitrogen-containing thin films in photomasks leads to the formation of foreign substances like ammonium sulfate during laser irradiation, especially with shorter wavelength exposure light sources, causing defects in semiconductor pattern transfer.
Innovation Solution
A lithography mask blank with an ammonium ion production preventing layer, either a thin film with less nitrogen or formed through heat treatment, is applied to the nitrogen-containing thin films to reduce ammonium ion concentration on the surface, thereby preventing the formation of ammonium sulfate.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a nitrogen-containing thin film is used to control phase shift and transmittance, then the film can achieve required optical properties and good acid/light resistance, but ammonium ions are produced on the film surface during laser irradiation leading to deposit formation
Solution Approach 1:
The thin film is divided into two functional layers: a nitrogen-containing layer that provides the required phase shift and transmittance properties, and a nitrogen-free or low-nitrogen surface layer that prevents ammonium ion production. This segmentation allows each layer to independently fulfill its specific function without compromising the other.
Solution Approach 2:
The surface layer is designed with different nitrogen content compared to the bulk film. The surface portion has reduced nitrogen content specifically to prevent ammonium ion generation during laser irradiation, while the underlying nitrogen-containing layer maintains the necessary optical properties. This local modification of composition addresses the harmful effect only where it occurs (at the surface) without affecting the overall film performance.
2Productivity
If high-energy laser light is used for exposure, then pattern transfer efficiency is improved, but chemical reactions on the photomask surface are accelerated causing accelerated deposit formation
Solution Approach 1:
A protective surface layer is formed in advance on the nitrogen-containing thin film before laser irradiation occurs. This surface layer acts as a barrier that prevents the laser-induced chemical reactions from generating ammonium ions and deposits, thereby enabling the use of high-energy laser light without the harmful side effects.
3Reliability
If sulfuric acid-based cleanser is used for photomask cleaning, then surface contamination is removed, but sulfuric acid ions remain on the photomask surface facilitating reactions with ammonium ions during laser irradiation
Solution Approach 1:
The nitrogen-free or low-nitrogen surface layer acts as an intermediary barrier between the sulfuric acid residues and the ammonium ion generation process. This surface layer prevents the interaction between residual sulfuric acid ions and any potential ammonium sources during laser irradiation, thereby eliminating the deposit formation pathway even when acid cleaning residues are present.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The ammonium ion concentration is significantly reduced, minimizing the production of foreign substances such as ammonium sulfate during laser exposure, thus enhancing the quality and reliability of pattern transfer in semiconductor manufacturing.
Implementation Method 1
an ammonium ion production preventing layer for preventing production of ammonium ions, which is formed on the nitrogen-containing thin film or at least at a surface portion of the nitrogen-containing thin film
Data Source
AI summary
A lithography mask blank used as a material for producing a lithography mask includes at least one thin film which is formed on a substrate and has a desired function. The blank has a nitrogen-containing thin film as the above-mentioned thin film and an ammonium ion production preventing layer for preventing production of ammonium ions, which is formed on the nitrogen-containing thin film or at least at a surface portion of the nitrogen-containing thin film and which is exposed on the surface of the lithography mask after the lithography mask is manufactured.